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    <meta charset='utf-8'>
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    <link rel='stylesheet' href='css/common.css'>

    <title>Spectator Mode</title>
  </head>
  <body>
    <header>
      <details open>
        <summary>Spectator Mode</summary>
        <p>
          This sample demonstrates how to render a separate, 3rd person view of
          the scene to an external monitor if one is available. This sample is
          not applicable to mobile or standalone devices.
          <a class="back" href="./">Back</a>
        </p>
      </details>
    </header>
    <main style='text-align: center;'>
    </main>
    <script type="module">
      import {WebXRButton} from './js/util/webxr-button.js';
      import {Scene} from './js/render/scenes/scene.js';
      import {Renderer, createWebGLContext} from './js/render/core/renderer.js';
      import {Gltf2Node} from './js/render/nodes/gltf2.js';
      import {mat4, quat} from './js/render/math/gl-matrix.js';
      import {InlineViewerHelper} from './js/util/inline-viewer-helper.js';
      import {QueryArgs} from './js/util/query-args.js';

      // If requested, use the polyfill to provide support for mobile devices
      // and devices which only support WebVR.
      import WebXRPolyfill from './js/third-party/webxr-polyfill/build/webxr-polyfill.module.js';
      if (QueryArgs.getBool('usePolyfill', true)) {
        let polyfill = new WebXRPolyfill();
      }

      const autoSpectate = QueryArgs.getBool('autoSpectate', false);

      // XR globals.
      let xrButton = null;
      let xrImmersiveRefSpace = null;
      let inlineViewerHelper = null;

      // WebGL scene globals.
      let gl = null;
      let renderer = null;
      let scene = new Scene();
      scene.addNode(new Gltf2Node({url: 'media/gltf/garage/garage.gltf'}));
      scene.standingStats(true);

      // Indicates if we are currently presenting a spectator view of the
      // scene to an external display.
      let spectatorMode = false;
      let spectatorButton = null;
      let spectatorProjectionMatrix = mat4.create();
      let spectatorQuat = quat.create();
      let headset = null;

      // Set up a view point in a corner of the garage scene near
      // near the ceiling and looking down at the origin/user.
      quat.rotateY(spectatorQuat, spectatorQuat, Math.PI * -0.25);
      quat.rotateX(spectatorQuat, spectatorQuat, Math.PI * -0.15);
      const spectatorTransform = new XRRigidTransform(
        {x: -1.75, y: 2.0, z: 1.75},
        {x: spectatorQuat[0], y: spectatorQuat[1], z: spectatorQuat[2], w: spectatorQuat[3]}
      );

      let mainElement = document.querySelector('main');

      function initXR() {
        xrButton = new WebXRButton({
          onRequestSession: onRequestSession,
          onEndSession: onEndSession
        });
        document.querySelector('header').appendChild(xrButton.domElement);

        if (navigator.xr) {
          navigator.xr.isSessionSupported('immersive-vr').then((supported) => {
            xrButton.enabled = supported;
          });

          navigator.xr.requestSession('inline').then(onSessionStarted);
        }
      }

      function initGL() {
        if (gl)
          return;

        gl = createWebGLContext({
          xrCompatible: true
        });
        document.body.appendChild(gl.canvas);

        onResize();
        window.addEventListener('resize', onResize);

        renderer = new Renderer(gl);
        scene.setRenderer(renderer);
      }

      function onRequestSession() {
        return navigator.xr.requestSession('immersive-vr', {
            requiredFeatures: ['local-floor']
        }).then((session) => {
          xrButton.setSession(session);
          session.isImmersive = true;
          onSessionStarted(session);

          // When the exclusive session starts, add a button to the page that
          // users can click to start the spectator mode. It's important to not
          // begin presenting spectator mode right away, because on some devices
          // that may mean doing additional work that the user can't see. By
          // requiring a button click first you're ensuring that the user CAN
          // still access the 2D page somehow.
          if (!autoSpectate) {
            spectatorButton = document.createElement('button');
            spectatorButton.textContent = 'Enable spectator mode';
            spectatorButton.addEventListener('click', onEnableSpectatorMode);
            mainElement.appendChild(spectatorButton);
            
            // Hide the non-exclusive session's output canvas so that we can see
            // the button.
            gl.canvas.style.display = 'none';
          } else {
            // This is really just for debugging, since it's useful to have
            // spectator mode start automatically in some testing scenarios.
            onEnableSpectatorMode();
          }
        });
      }

      function onSessionStarted(session) {
        session.addEventListener('end', onSessionEnded);

        initGL();
        scene.inputRenderer.useProfileControllerMeshes(session);

        let glLayer = new XRWebGLLayer(session, gl);
        session.updateRenderState({ baseLayer: glLayer });

        let refSpaceType = session.isImmersive ? 'local-floor' : 'viewer';
        session.requestReferenceSpace(refSpaceType).then((refSpace) => {
          if (session.isImmersive) {
            xrImmersiveRefSpace = refSpace;
          } else {
            inlineViewerHelper = new InlineViewerHelper(gl.canvas, refSpace);
            inlineViewerHelper.setHeight(1.6);
          }

          session.requestAnimationFrame(onXRFrame);
        });
      }

      function onEndSession(session) {
        session.end();
      }

      function onSessionEnded(event) {
        if (event.session.isImmersive) {
          xrButton.setSession(null);

          // When we exit the inline session stop presenting the spectator view.
          if (spectatorMode) {
            spectatorMode = false;
          }

          // Remove the spectator button if needed.
          if (spectatorButton) {
            mainElement.removeChild(spectatorButton);
            spectatorButton = null;
          }

          // Show the WebGL canvas again if it was hidden.
          gl.canvas.style.display = '';
        }
      }

      // Called when the user clicks the button to enable spectator mode.
      function onEnableSpectatorMode() {
        spectatorMode = true;

        // Show the WebGL canvas
        gl.canvas.style.display = '';

        onResize();

        // Remove the spectator button, since it's no longer needed. You could
        // alternately change the button's function to disable spectator mode.
        if (spectatorButton) {
          mainElement.removeChild(spectatorButton);
          spectatorButton = null;
        }

        // Load up a mesh that we can use to visualize the headset's pose.
        if (!headset) {
          headset = new Gltf2Node({url: 'media/gltf/headset/headset.gltf'});
          scene.addNode(headset);
        }
      }

      function onResize () {
        let scaleFactor = window.devicePixelRatio;
        if (spectatorMode) {
          // The spectator view does take time to render, and can impact the
          // performance of the in-headset view. To help mitigate that, we'll
          // draw the spectator view at half the native resolution.
          scaleFactor /= 2.0;
        }
        gl.canvas.width = (gl.canvas.offsetWidth * scaleFactor);
        gl.canvas.height = (gl.canvas.offsetHeight * scaleFactor);
      }

      function onXRFrame(t, frame) {
        let session = frame.session;
        let refSpace = session.isImmersive ?
                         xrImmersiveRefSpace :
                         inlineViewerHelper.referenceSpace;
        let pose = frame.getViewerPose(refSpace);

        scene.startFrame();

        session.requestAnimationFrame(onXRFrame);

        scene.updateInputSources(frame, refSpace);

        scene.drawXRFrame(frame, pose);

        // If spectator mode is active, draw a 3rd person view of the scene to
        // the WebGL context's default backbuffer.
        if (spectatorMode && pose) {
          // Bind the WebGL context's default framebuffer, so that the rendered
          // content shows up in the canvas element.
          gl.bindFramebuffer(gl.FRAMEBUFFER, null);

          // Clear the framebuffer
          gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

          // Set the viewport to the whole canvas
          gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);

          // Set up a sensible projection matrix for the canvas
          mat4.perspective(spectatorProjectionMatrix, Math.PI*0.4,
                           gl.drawingBufferWidth / gl.drawingBufferHeight,
                           session.renderState.depthNear,
                           session.renderState.depthFar);

          // Update the headset's pose to match the user's and make it visible
          // for this draw.
          if (headset) {
            headset.visible = true;
            headset.matrix = pose.transform.matrix;
          }

          // Draw the spectator view of the scene.
          scene.draw(spectatorProjectionMatrix, spectatorTransform);

          // Ensure the headset isn't visible in the VR view.
          if (headset) {
            headset.visible = false;
          }
        }

        scene.endFrame();
      }

      // Start the XR application.
      initXR();
    </script>
  </body>
</html>
